1. Field of Invention
The present invention relates to a motor control apparatus and a control method thereof.
2. Related Art
A motor is an important device for rotating or moving an object. Moreover, the working efficiency can be enhanced by using the suitable motor. Regarding to the motor applied to a fan, the motor can drive the impeller of the fan to rotate so as to generate airflows or dissipate heats. If the motor properly functions, the heat dissipation efficiency of the fan can be maintained.
In general, a motor is constituted by a stator and a rotor disposed opposite to each other. The rotor can rotate with respect to the stator by the magnetic force and magnetic field change. The magnetic field change represents the phase commutation of the magnetic poles of the motor. The conventional motor usually utilizes a brush and a commutator to carry out the phase commutation. However, the high speed rotation of the rotator causes the serious friction between the brush and commutator, which may result in the damage of the motor. Accordingly, the electronic commutator is used to carry out the phase commutation in the present motor. The electronic commutator mainly utilizes a Hall sensor to sense the positions of the magnetic poles of the motor (or the magnetic field change) so as to determine the position of the rotor. Then, a control signal is generated to control the switch of the coil current in the stator, thereby achieving the phase commutation.
The above-mentioned method of sensing the magnetic field change by the Hall sensor is related to the rotation speed of the motor and the positions of the Hall sensor. Thus, the Hall sensor must be disposed at the optimum position so as to process the precisely sensing. In the present application, it is most commonly used way to control the rotation speed of the motor. When the rotation speed of the motor is changed, the Hall sensor can not be adjusted to the optimum position automatically, so that it may sense the leading or lagging magnetic field phase and output improper control signal. In this case, the phase commutation is not smooth and the motor may generate noise. When the motor is applied to a fan, the heat dissipation efficiency of the fan will be worse.